Messages in this thread | | | From | Dmitry Vyukov <> | Date | Mon, 11 Jun 2018 07:49:41 +0200 | Subject | Re: WARNING: kmalloc bug in xdp_umem_create |
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On Sun, Jun 10, 2018 at 3:03 PM, Björn Töpel <bjorn.topel@gmail.com> wrote: >> On 2018/06/10 20:52, Dmitry Vyukov wrote: >> > On Sun, Jun 10, 2018 at 11:31 AM, Björn Töpel <bjorn.topel@gmail.com> wrote: >> >> Den sön 10 juni 2018 kl 04:53 skrev Tetsuo Handa >> >> <penguin-kernel@i-love.sakura.ne.jp>: >> >>> >> >>> On 2018/06/10 7:47, syzbot wrote: >> >>>> Hello, >> >>>> >> >>>> syzbot found the following crash on: >> >>>> >> >>>> HEAD commit: 7d3bf613e99a Merge tag 'libnvdimm-for-4.18' of git://git.k.. >> >>>> git tree: upstream >> >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1073f68f800000 >> >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=f04d8d0a2afb789a >> >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=4abadc5d69117b346506 >> >>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >> >>>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13c9756f800000 >> >>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16366f9f800000 >> >>>> >> >>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> >>>> Reported-by: syzbot+4abadc5d69117b346506@syzkaller.appspotmail.com >> >>>> >> >>>> random: sshd: uninitialized urandom read (32 bytes read) >> >>>> random: sshd: uninitialized urandom read (32 bytes read) >> >>>> random: sshd: uninitialized urandom read (32 bytes read) >> >>>> random: sshd: uninitialized urandom read (32 bytes read) >> >>>> random: sshd: uninitialized urandom read (32 bytes read) >> >>>> WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996 >> >>>> Kernel panic - not syncing: panic_on_warn set ... >> >>> >> >>> syzbot gave up upon kmalloc(), but actually error handling path has >> >>> NULL pointer dereference bug. >> >>> >> >> >> >> Thanks Tetsuo! This crash has been fixed by Daniel Borkmann in commit >> >> c09290c56376 ("bpf, xdp: fix crash in xdp_umem_unaccount_pages"). >> > >> > Let's tell syzbot about this: >> > >> > #syz fix: bpf, xdp: fix crash in xdp_umem_unaccount_pages >> > >> > >> Excuse me, but that patch fixes NULL pointer dereference which occurs after kmalloc()'s >> "WARNING: CPU: 1 PID: 4537 at mm/slab_common.c:996 kmalloc_slab+0x56/0x70 mm/slab_common.c:996" >> message. That is, "Too large memory allocation" itself is not yet fixed. > > The code relies on that the sl{u,a,o}b layer says no, and the > setsockopt bails out. The warning could be opted out using > __GFP_NOWARN. Is there another preferred way? Two get_user_pages > calls, where the first call would set pages to NULL just to fault the > region? Walk the process' VMAs? Something else?
Hi Björn,
Yes, either __GFP_NOWARN for allocations with user-controllable size or stricter custom limit (if we don't want current sla/u/ob implementation details to be part of public kernel interface).
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